This invention relates to fine spherical powder particles and to the process for producing the particles which involves mechanically reducing the size of a starting material followed by high temperature processing to produce fine spherical particles. More particularly the high temperature process is a plasma process.
U.S. Pat. No. 3,909,241 to Cheney et al relates to free flowing powders which are produced by feeding agglomerates through a high temperature plasma reactor to cause at least partial melting of the particles and collecting the particles in a cooling chamber containing a protective gaseous atmosphere where the particles are solidified.
Fine spherical metal particles such as iron, cobalt, nickel, chromium, and alloys thereof are useful in applications such as filters, precision press and sinter parts, and injection molded parts. Typical alloys include but are not limited to low alloy steels, stainless steels, tool steel powders, nickel and cobalt based superalloys. In such applications the powders are consolidated by standard methods such as hot or warm extrusion, PM forging and metal injection molding, or pressing and sintering.
Some of the better commercial processes for producing such metal powder particles are by gas or water atomization. Only a small percentage of the powder produced by atomization is less than about 20 micrometers. Therefore, yields are low and metal powder costs are high as a result and in the case of water atomization, the powder is often not spherical.
In European Patent Application No. WO8402864 published Aug. 2, 1984, there is disclosed a process for making ultra-fine powder by directing a stream of molten droplets at a repellent surface whereby the droplets are broken up and repelled and thereafter solidified as described therein. While there is a tendency for spherical particles to be formed after rebounding, it is stated that the molten portion may form elliptical shaped or elongated particles with rounded ends.
A process for efficiently producing fine spherical metal particles would be an advancement in the art.